Recessed gate silicon-on-insulator floating body device with self-aligned lateral isolation
View Patent ↗Embodiments of a manufacturing process for recessed gate devices on silicon-on-insulator (SOI) substrate with self-aligned lateral isolation are described. This allows the creation of true in-pitch recessed gate devices without requiring an extra isolation dimension. A lateral isolation trench is formed between pairs of recessed gate devices by etching the silicon-on-insulator area down to a buried oxide layer on which the silicon-on-insulator layer is formed. The position of the trench is self-aligned and defined by the gate width and the dimension of spacers disposed on either side of the gate. The isolation trench is filled with a dielectric material and then etched back to the middle of the SOI body and the remaining volume is filled with a doped conductive material. The doped conductor is subject to a thermal cycle to create source and drain regions of the device through out-diffusion of the doped material.
1. A recessed gate device comprising:
an oxide layer;
a silicon layer formed on the oxide layer, the silicon layer having source and drain regions formed therein;
a recessed gate region formed in the silicon layer, wherein a bottom of the recessed gate region is disposed below a bottom of the source and drain regions; and
at least one spacer formed on the silicon layer, wherein a first side of the at least one spacer defines an upper portion of the recessed gate region, wherein a second side of the at least one spacer defines an upper region of an isolation trench, and wherein the at least one spacer is disposed apart from a lower portion of the recessed gate region.
2. The recessed gate device of claim 1 , wherein the isolation trench is partially filled with a dielectric material.
3. The recessed gate device of claim 2 , wherein the dielectric material fills the isolation trench such that a top of the dielectric material is disposed below a top of the silicon layer.
4. The recessed gate device of claim 2 , wherein the dielectric material fills the isolation trench such that a top of the dielectric material is disposed above the bottom of the recessed gate region.
5. The recessed gate device of claim 2 , further comprising a doped conductive material disposed above the dielectric material in the isolation trench.
6. The recessed gate device of claim 5 , wherein the doped conductive material is doped polysilicon.
7. The recessed gate device of claim 5 , wherein the bottom of the source region is disposed below a top of the dielectric material.
8. The recessed gate device of claim 7 , wherein the source region extends from the doped conductive material to the recessed gate region.
9. The recessed gate device of claim 7 , wherein the source region extends from the doped conductive material but not to the recessed gate region.
10. The recessed gate device of claim 7 , wherein the source region is formed by out-diffusing the doped conductive material via at least one thermal cycle.
11. The recessed gate device of claim 7 , wherein the bottom of the source region is disposed above a top of the dielectric material.
12. The recessed gate device of claim 7 , wherein the bottom of the drain region is disposed below a top of the dielectric material.
13. The recessed gate device of claim 12 , wherein the drain region extends from the doped conductive material to the recessed gate region.
14. The recessed gate device of claim 12 , wherein the drain region extends from the doped conductive material but not to the recessed gate region.
15. The recessed gate device of claim 12 , wherein the drain region is formed by out-diffusing the doped conductive material via at least one thermal cycle.
16. The recessed gate device of claim 12 , wherein the bottom of the drain region is disposed above a top of the dielectric material.
17. The recessed gate device of claim 1 , wherein the oxide layer is formed on a silicon substrate.
18. The recessed gate device of claim 1 , wherein the at least one spacer comprises at least two spacers defining at least two sides of the upper region of the recessed gate region.
19. The recessed gate device of claim 1 , wherein the recessed gate region comprises a gate separated from the silicon layer by an insulative layer.
20. The recessed gate device of claim 1 , wherein the isolation trench is tapered to be narrower at a bottom of the isolation trench than at a top of the isolation trench.